Process of making nitrites.



UNTTED STATES PATENT UEEICE.

RUDOLF l-IEINZ, OF HANOVER, GERMANY, ASSIGNOR TO GEBRUDER FLIOK, OFOPLADEN, GERMANY.

PROCESS OF MAKING NITRITES.

SZECIFICATION forming part of Letters Patent No. 670,021, dated March19, 1901.

Application filed September 10,1900. Serial No. 29,594. (No specimens.)

T0 aZZ whom, it may concern:

Be it known that I, RUDOLF HEINZ, a subject of the King of Saxony,residing at Hanover,Province of Hanover,Empire of Germany, have inventednew and useful Improvements in Processes for the Manufacture ofNitrites, of which the following is a full specification.

There have been suggested a great many methods for the manufacture ofnitrites from nitrates which on carrying out in practice have not proveda success from a commercial point of view. Practically all these methodswere based on the reduction of nitrates, or rather of the acid radicalof nitrates, by means of the usual reducing agents.

The object of the present invention is also the reduction of the acidradical of nitrates; but it is proposed to employ for that purposesulfur dioxid in a gaseous state. It was ascertained by repeatedexperiments that if gaseous sulfur dioxid be passed over a mixture of anitrate and an oxid, principally an oxid of an alkali or an alkalineearth heated up to a point where the fluxed mass becomes sintered, thenitrate is completely reduced to a nitrite, whereas the sulfur dioxid isoxidized to s ulfuric acid,which, in statu nascendt', combines with thefree base present. The base may also be present as a carbonate, althoughthe free oxid or its hydrate will prove more eificient. The reactiontaking place may be represented by the following equations,where sodiumnitrate and caustic lime may be supposed to be employed in the process:

NaNO +SO =NaNO +SO SO +CaO=CaSO or, expressed in one single equation,

NaNO +OaO+SO :NaNO OaSO From the product of reaction obtained,whichrepresents a mixture of sodium nitrite and calcium sulfate, the nitriteis lixiviated with water and the solution worked up for pure nitrite inthe usual manner, whereas calcium sulfate is left as an insolubleresidue.

If bases be employed the sulfates of which are soluble in waterforinstance, alkali hydrates or carbonates-there results an alkalinesulfate, which makes the separation of the nitrite and its preparationin a pure state a somewhat diiiicult task. For this reason it ispreferable to employ the oxids of alkaline earths in the process.Anyhow, if properly carried out, the decomposition and reduction of thenitrate is complete. The yield is nearly a theoretical one, and theseparation from the insoluble sulfate is a simple operation, so that thepreparation of a pure nitrite offers no diiiiculties. It is also of thegreatest importance that the sulfur dioxid is as nearly free from air(oxygen) as possible, so that no secondary oxidation of the sulfurdioxid may take place, because the sulfuric acid thus formed would actinjuriously on the nitrate or even the nitrite freshly formed, wherebythe yield would considerably decrease.

The quantity of the base to be added is not confined to molecularproportions. An excess of the base is even profitable.

A mode of manufacturing nitrites by fusing a mixture of equal moleculesof anhydrous potassium sulfite and potassium nitrate has been suggestedby Etard (Jahresbar. d. Ohemt'e, 1877, page 239) where nitrite and analkaline sulfate is formed according to the following equation:

KNO +K SO =KNO +K SO This mode of preparation is, however, not based onthe same principle as the present process, as it must be supposed thatby using sulfur dioxid a direct reduction of the acid radical of thenitrate is efiected. In order to prove that supposition, I may mentionthat if an intimate mixture of sodium nitrate and calcium sulfite beheated up to the fusingpoint numerous sparks issue from the mass,showing that a loss of oxygen has taken place, whereas on passing sulfurdioxid over a heated mixture of a nitrate and calcium hydrate no suchloss occurs. As a consequence the yield of nitrite is much greater inthe second case than when usinga sulfite in place of sulfur dioxid.

The present process is carried out on a large scale thus: Caustic limeis very intimately mixed with a nitrate. This is eifected by slakingcaustic lime with a concentrated solution of potassium nitratet. (2.,one hundred and sixty kilos caustic lime are slaked with a veryconcentrated solution of two hundred kilos sodium nitrate. This mixtureis heated in suitable retorts until the mass is sintered, sulfur dioxidfree from air being passed over the mixture all the While. The processis finished when all the nitrate has been reduced to nitrite. action istaken up with hot Water and the solution of the nitrite filtered fromthe insoluble residue consisting of calcium sulfate. The

filtrate is Worked up for pure nitrite by boiling down andcrystallization.

What I claim isl. A process for the manufacture of nitrites The productof re consisting in passing sulfur dioxid as free .fl'OlI] air aspossible over a highly-heated mix-

